BySteve Peoples, Associated PRessMarch 19, 2012

The intrepid Black Knight refuses to give up, even after losing several limbs, in the 1975 movie "Monty Python and the Holy Grail." Mitt Romney campaign officials are calling Rick Santorum the Black Knight of the GOP race.

Monty Python and the Holy Grail

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Vernon Hills, Illinois — Mitt Romney's increasingly confident campaign is intensifying calls — publicly and privately — for his Republican opponents to concede defeat in the presidential nomination battle, even before Illinois voters have their say Tuesday in the campaign's next big contest.

Romney extended his delegate lead Sunday in Puerto Rico, where he trounced rival Rick Santorum and scored all 20 of the Caribbean island's delegates. Romney has collected more delegates than his opponents combined and is poised to win the delegate battle in Illinois, even if he loses the popular vote, thanks to missteps by Santorum's shoestring operation.

Romney's wife, Ann, declared Sunday night in suburban Illinois that the time has come for her husband's rivals to quit the race.

"We need to send a message that it's time to coalesce," she said, Mitt at her side. "It's time to get behind one candidate and get the job done so we can move on to the next challenge, bringing us one step closer to defeating Barack Obama."

Brushing aside skepticism from the party's right flank, Romney aides have been emphasizing their overwhelming mathematical advantage in the race to 1,144 delegates — the number needed to clinch the GOP presidential nomination and face President Barack Obama in the fall.

Santorum has all but conceded he cannot earn enough delegates to win, but claimed he was in contest for the long haul because Romney is a weak front-runner.

He said Monday that he'll "go out and compete in every state, calling Illinois a "two-person race."

"What I've said is, I think it's going to be very difficult as this goes on for anybody to get that magic number" to clinch the nomination, Santorum said in an interview on CBS's "This Morning."

He called Romney a "big-government heavyweight," responding on MSNBC Monday to the Massachusetts governor's assertion that he couldn't match up on economic expertise. Santorum told CBS he thinks the chances of a brokered GOP convention in August "are increasing."

In nationally broadcast remarks Sunday, Santorum sidestepped when asked if he would fight Romney on the convention floor if he failed before August to stop the former Massachusetts governor from getting the required number of delegates.

Romney aides privately likened the situation to the Black Knight in "Monty Python and the Holy Grail" who loses his arms and legs in battle with King Arthur but insists he has only a flesh wound. The Romney camp suggested that Tuesday's performance would extend Romney's delegate advantage, even if he loses the popular vote.

Santorum cannot win at least 10 of the state's 54 delegates because his campaign failed to file the paperwork.

One Romney aide recently said it would take "an act of God" for Santorum to earn enough delegates to prevail.

"Mitt's going to do well," said Romney's Illinois chairman Dan Rutherford, the state treasurer. "I think he will do better than the other three people. ... But my focus is on the delegates because that's really what the game is all about."

Polls suggest the Illinois race is close. And even at a Romney campaign stop Sunday, voters were divided.

"I'm leaning toward Santorum, but I wanted to hear him in person," said Nichole Warren, a 32-year-old stay-at-home mom from nearby South Beloit. "I hear (Romney) talk and I hear a lot of Obama in him, and that scares me."

But Sid Haffenden, a 61-year-old retired toll-way worker, said, "Santorum has too much baggage." He added, "I want a businessman."

Santorum is not giving up. He will spend Monday and Tuesday courting Illinois voters. Santorum plans to host four rallies Monday.

While offering a confident front, Romney cut short campaign plans in Puerto Rico over the weekend to spend more time in the state. He arrived Saturday night and plans to stay in the state through Tuesday night.

At this rate, Romney is on pace to capture the nomination in June unless Santorum or former House Speaker Newt Gingrich is able to win decisively in the coming contests.

Both have said they would stay in the race and perhaps force the nomination to a fight at the GOP's convention in Tampa if Romney doesn't amass enough delegates to arrive with a mandate. That would turn the convention into an intra-party brawl for the first time since 1976.

Including Puerto Rico's results, Romney has now collected 521 delegates, compared to Santorum's 253, Gingrich's 136 and Paul's 50, according to The Associated Press count.